The present disclosure relates generally to directional drilling of boreholes in the earth, and more particularly down-hole assemblies employed for drilling boreholes in subsurface formations, in the search for hydrocarbons such as oil and natural gas.
It is sometimes necessary to drill in directions other than the vertical direction while exploring for hydrocarbons. Such exploration activity is known as directional drilling. Various tools have been employed to achieve directional drilling in the past. For example, a down-hole motor assembly for alternately drilling straight and inclined borehole sections includes a bent sub and/or housing that is installed downstream of the drill string when it is necessary to drill the inclined borehole section. Use of such motors typically involves time consuming and expensive removal and replacement of down-hole assembly components necessary to drill vertical or straight sections of the borehole.
Another down-hole assembly for alternately drilling straight and inclined borehole sections includes a bearing assembly that supports an output shaft, which is pivotably connected to a motor housing. A remotely controlled positioning system is used to vary the angle between the housing and the output shaft to drill straight or inclined borehole sections as desired. However, the fragility of the pivots between motor housing and the output shaft and the complexity of the remotely controlled positioning system are undesirable.